Ultrasonic imaging has proved useful in the medical arts because of its ability to provide structural information about a patient's subcutaneous sound scatterers (organs, blood, bones, etc.). Typically, ultrasonic imaging systems (1) transmit ultrasonic energy from a transducer through a patient's skin, (2) electrically process echoes from the patient's subcutaneous sound scatterers, and (3) produce an image of those sound scatterers on a display device. It is highly desirable to increase the image detail so that improved analysis of the sound scatterers is possible. However, before increased image detail can be achieved, the structural information from the sound scatterers must be increased.
One method of increasing the structural information is to focus the transmitted ultrasonic energy into a small cross-sectional area. Focused ultrasonic energy, hereinafter referred to as a beam, increases the structural information by increasing the energy applied to sound scatterers near the beam's focal point while reducing the energy applied to adjacent tissues, thereby providing increased echo discrimination. However, as is well known to those in the art, a focused beam has its ultrasonic energy contained in a beam profile that widens as the distance from the beam's focal point increases. Therefore, at locations remote from the beam's focal point, the advantages of focusing are lost since the beam's cross-sectional area necessarily increases.
Some conventional ultrasound imaging systems have sought to overcome focusing limitations by combining echoes from multiple beams, each having a different focal length, to form a composite image. While systems using multiple beams have proved successful, the combining of the echoes typically produces undesirable bright or dark lines, called image artifacts, in interstitial areas between the beam's focal points.
Therefore, it is clear that there has existed a need for a system that smoothly blends echoes resulting from a plurality of beams having different focal points to form a composite image having reduced image artifacts.